Transcript Homeostasis
Homeostasis • Homeostasis is the maintenance of equilibrium, or constant conditions, in a biological system by means of automatic mechanisms. • In the 19th century, the French physiologist Claude BERNARD noted the constancy of the chemical composition and physical properties of blood and other body fluids. • The term homeostasis was coined by the 20th-century American physiologist Walter B. Cannon, who refined and extended the concept of self-regulating mechanisms in living systems. Homeostasis of Body Fluids • Fluid Compartments: -ICF: intracellular fluid = within the cell -ECF: extracellular fluid = outside the cells - aka: interstitial fluid Composition of fluids change as substances move between compartments: nutrients, oxygen, ions and wastes move in both directions Neural and endocrine control • Homeostasis is the process of maintaining a controlled condition - Sensory receptors detect change in a monitored variable ( CO2 levels, glucose levels, water levels, temperature) -nervous system and/or endocrine system responds Feedback Loop • All homeostatic mechanisms use negative feedback to maintain a constant value (called the set point). • Negative feedback means that whenever a change occurs in a system, the change automatically causes a corrective mechanism to start, which reverses the original change and brings the system back to normal. • In a system controlled by negative feedback, the level is never maintained perfectly, but constantly fluctuates about the set point. • An efficient homeostatic system minimizes the size of the fluctuations. • Negative feedback applies to electronic circuits and central heating systems as well as to biological systems. Thermoregulation • One of the most important examples of homeostasis is the regulation of body temperature. • Animals that maintain a fairly constant body temperature (birds and mammals) are called homeotherms • Homeotherms maintain their body temperatures at around 37°C. Why? • Animals that have a variable body temperature (all others) are called poikilotherms. -In humans, temperature homeostasis is controlled by the thermoregulatory centre in the hypothalamus. -The thermoregulatory centre receives input from two sets of thermoreceptors: a. receptors in the hypothalamus itself monitor the temperature of the blood as it passes through the brain (the core temperature) b. receptors in the skin monitor the external temperature. -The thermoregulatory centre sends impulses to several different effectors to adjust body temperature Regulation of Blood Glucose • The body requires glucose in order to create ATP. The amount of ATP required will fluctuate, and therefore the body regulates the availability of glucose. • Two hormones are responsible for controlling the concentration of glucose in the blood: Insulin and Glucagon Water Regulation Osmoregulation • Osmoregulation is the regulation of water concentrations in the bloodstream, effectively controlling the amount of water available for cells to absorb. Osmoregulation: water balance Mechanism of Osmoregualtion • Osmoreceptors that are capable of detecting water concentration are situated on the hypothalamus next to the circulatory system. • The hypothalamus sends chemical messages to the pituitary gland next to it. • The pituitary gland secretes anti-diuretic hormone (ADH), which targets the kidney that are responsible for maintaining water levels. • When the hormone reaches its target tissue, it alters the tubules of the kidney to become more / less permeable to water • If more water is required in the blood stream, high concentrations of ADH make the tubules more permeable. • If less water is required in the blood stream, low concentrations of ADH make the tubules less permeable.